- Characteristics of SF6 application in electric gas filled cabinet industry
- 。SF6 is an artificial inert gas with a molecular weight of 146. It has good electrical insulation performance and excellent arc extinguishing performance. Its electric strength is 2.5 times that of nitrogen under the same pressure, its breakdown voltage is 2.5 times that of air, and its arc extinguishing capacity is 100 times that of air. It is a new generation of ultra-high voltage insulating medium material superior to that between air and oil. It is widely used in high and medium voltage power equipment.
- The pure SF6 is non-toxic, but the products may be mixed with toxic gases, which may also produce toxic gases under the action of high-temperature arc.
- SF6 is a greenhouse gas. It is one of the six greenhouse gases prohibited by the Kyoto Protocol to the United Nations Framework Convention on Climate Change formulated in December 1999 (entered into force on February 16, 2005).
- power switch cabinet sealing test standard
Requirements for sealing test of SF6 enclosed composite apparatus in 13.0.4 of GB50150-2016 Standard for Hand over Test of Electrical Equipment in Electrical Equipment Installation Engineering:
- The leak detector with sensitivity no less than 1X10-6 (volume ratio) can be used to detect the sealing parts of each air chamber and pipe joints, and the leak detector shall not alarm;
- If necessary, the local binding method can be used for gas leakage measurement. The annual leakage rate of each air chamber shall not be greater than 1%, and the 750 voltage level shall not be greater than 0.5% based on the conversion of 24h gas leakage;
Application analysis
- The first test method belongs to fixed-point leak detection method. The detection result will be greatly affected by the operator, and the overall leakage rate cannot be detected;
- The second test method is widely used in the early stage. SF6 leakage detector is used for detection, with the highest accuracy of 1ppm and alarm leakage rate of 30ppm (reference value).
- At present, vacuum chamber helium detection equipment is mainly used in the industry, which can detect the overall leakage rate. If leakage is found, it can also be specific. This method has the characteristics of energy conservation and environmental protection, high detection accuracy, high automation level and obvious improvement of beat.
- Sealing test standard for SF6 high-voltage switch housing
Requirements for sealing test in 7.4 of GB7674-2008 Gas Metal Enclosed Switchgear with Rated Voltage of 72.5KV and Above:
- GB/T 11022-1999的7.4适用，并作如下补充：of GB/T 11022-1999 is applicable and supplemented as follows:
A leak detector can be used for leak detection. The sensitivity of the leak detection device shall be at least 10-2Pa.cm3/s. If the leak detection device detects a leak, the leak shall be measured quantitatively using the binding method specified in GB/T 11023;
- GB/T 11022-2011（代替GB/T 11022-1999）的7.5.3：
7.5.3 of GB/T 11022-2011 (replacing GB/T 11022-1999):
A leak detector can be used to detect the leakage rate of the inflation system, and the sensitivity of the leak detector shall be at least 10-8Pa. m3/s.
应用分析：
Application analysis:
- This test method is one of the most widely used methods at present. SF6 leak detector is used for detection. The accuracy of the leak detector is required to be no less than 10E-2Pa. cm3/s (i.e. 10E-8Pa. m3/s)
- At present, another method widely used in the industry to detect helium filling is divided into two methods: suction gun type and vacuum chamber type, which are suction gun type leak detection point and vacuum chamber type leak detection. Compared with SF6, helium detection has the characteristics of energy conservation, environmental protection and high detection accuracy. The vacuum chamber type has the characteristics of high automation level and overall quantitative detection.
- Application characteristics of helium leak detection
Helium is a colorless, tasteless, non-toxic monatomic gas with inert chemical properties, molecular weight of 4 and volume content of about 5ppm in the air.
Application analysis
- Helium has small molecular weight, strong diffusion and high permeability, which means it can pass through tiny holes.
- The volume content of helium in the air is about 5ppm, which indicates that the helium content in the normal air environment is very small, that is, the helium background is very good.
- Helium is a non-toxic, colorless and tasteless inert gas, which means that it can exist in all objects as a medium under normal conditions without reaction.
- It is easy to distinguish from other substances in the mass spectrometer spectrogram.
- Based on the above characteristics, helium, as a tracer gas for leak detection, is the best choice
- Main technical parameters of Anhui Daxin DXF-620 vacuum chamber helium leak detection and recovery system
1) The internal and external pressure difference of the workpiece: ≤ 0.05MPa, and the alarm setting value of the pressure difference exceeding the range is adjustable.
2) Leakage rate of workpiece detection: SF6 annual leakage rate 0.1%/year;
3) Maximum detection accuracy of leak detector: 10E-13Pa. m3/s;
4) Leakage detection time: ≤ 45min/box (SF6 gas charging cabinet, conventional 6 units);
5) Helium recovery rate: ≥ 95%;
6) Opening pressure of leak detector (vacuum box): ≤ 20pa (ultimate vacuum 1Pa);
7) The equipment has the function of manually searching for leakage points outside the box.
8) Size and volume of vacuum chamber inner chamber: customized according to the size of the workpiece to be inspected
9) Number of workpiece interfaces in the vacuum box: 2 independent connectors in the vacuum chamber can detect 2 small workpieces at the same time.
10) Key components such as leak detector, vacuum pump, vacuum gauge, leak mark, solenoid valve, sensor and compressor are imported first-line brands.